In automatic transmissions known from practice which, besides frictional shift elements, also comprise interlocking shift elements for obtaining various gear ratios, in unfavorable operating conditions the possibility exists that during a change in the operating condition of the automatic transmission or during a gearshift an interlocking shift element cannot be changed to the desired extent from an open operating condition, during which the shift element halves of the interlocking shift element are out of engagement, to a closed operating condition in which the shift element halves are connected rotationally fixed with one another in an interlocked manner.
This, for example, is the case in the event of an intermediate operating condition of an interlocking shift element, in which the halves of the shift element are in contact with one another without a rotationally fixed connection in a so-termed tooth-on-tooth position and are rotating at the same speed, so that between the shift element halves of the interlocking shift element there is too small a rotational speed difference for the desired interlock in the area of the interlocking shift element. During such an intermediate operating condition of an interlocking shift element, in the area of the interlocking shift element there is a frictional connection between its shift element halves, which is suddenly broken only when a certain load point is exceeded, so the interlock is produced in the area of the shift element, undesirably, at a moment which can only be determined in advance with difficulty.
Furthermore, in the present context operating conditions of interlocking shift elements are also classified as intermediate operating conditions, during which there is too high a speed difference between the shift element halves of an interlocking shift element, which opposes the formation of an interlock. Depending on the design of the drive train, this is the case particularly after operation of a vehicle first begins.
From DE 197 56 637 A1 a shifting device is known for connecting components of a transmission rotating at different speeds to at least one shifting group, such that the shifting device is actuated by a control fluid. During operation of the transmission device a current operating condition of the shifting group containing at least one interlocking shift element is monitored, and if a tooth-on-tooth position of the teeth to be interlocked occurs, a synchronizing force in the area of the interlocking shift element is minimized, in order to produce a drag torque during the synchronization of the interlocking shift element to be closed, by virtue of which the tooth-on-tooth position should be eliminated.
The proposed procedure for eliminating a tooth-on-tooth position in the area of an interlocking shift element presupposes an exact knowledge of the current operating condition of the interlocking shift element, which can only be determined with considerable difficulty, in order to minimize the synchronizing force to the extent required for resolving the tooth-on-tooth position.